1. Field of the Invention
The present invention relates to a hydrogenolysis catalyst.
2. Background Art
Hydrogenolysis has been used as a means for synthesizing intermediate chemical products. Hydrodesulfurization reaction, dehalogenation reaction, ester hydrogenolysis, debenzylation reaction, and the like can be given as types of hydrogenolysis reactions. As known catalysts, Raney nickel is used in the hydrodesulfurization reaction, Pd/carbon and Pt/carbon are used in the dehalogenation reaction, and PtO2 and Pd/carbon are used in ester hydrogenolysis. Also, as known catalysts for the debenzylation reaction, Pd/carbon, Pd black, Raney nickel, Rh/carbon, Ru/carbon, Re/carbon (Japanese Patent Application Laid-open No. 87542/1987), Pd/carbon, palladium oxide, palladium black or palladium chloride (Japanese Patent Application Laid-open No. 47143/1991), PtO2, Pd/carbon, Rh/carbon, RuO2, and the like (Japanese Patent Application Laid-open No. 99036/1991), and Pd/carbon (Japanese Patent Application Laid-open No. 330331/1998) have been disclosed.
The above hydrogenolysis catalysts, however, fail to provide sufficient activity at low temperatures. Also, the use of these catalysts during a debenzylation reaction of a compound in which nitrogen combines with a benzyl group gives rise to a problem that the reaction does not proceed easily. Therefore, a catalyst exhibiting high hydrogenolysis performance under these conditions has been demanded.
In order to solve the above problems, the objective of the present invention is to provide a catalyst possessing a high activity at low temperatures and high hydrogenolysis performance during the debenzylation reaction of a compound in which nitrogen combines with a benzyl group.
As a result of extensive studies in order to find a catalyst possessing high hydrogenolysis performance, the inventors of the present invention have discovered that a catalyst prepared by combining a particular noble metal element with a compound containing divalent palladium can solve the above problems. This finding has led to the completion of the present invention.
Specifically, the present invention provides a hydrogenolysis catalyst comprising (a) a component comprising at least one compound selected from the group consisting of palladium oxide, palladium oxide monohydrate, and palladium hydroxide, wherein the oxidation state of palladium is divalent, and (b) a component comprising at least one element selected from the group consisting of Pt, Ru, Rh, Ir, and Au, both carried on a non-organic porous substance.
Other objects, features and advantages of the invention will hereinafter become more readily apparent from the following description.
The hydrogenolysis catalyst of the present invention (hereinafter referred to as xe2x80x9ccatalystxe2x80x9d) is prepared by causing the above components (a) and (b) to be carried on a non-organic porous substance by a conventional method.
The component (a) of the catalyst of the present invention comprises at least one of palladium oxide (PdO), palladium oxided monohydrate (PdO H2O), and palladium hydroxide (Pd(OH)2), wherein the oxidation state of Pd is divalent. PdO, PdO H2O and Pb(OH)2 may be used either individually or in a combination of two or more in component (a).
A major portion of the Pd contained in the component (a) of the present invention must be divalent. If a major portion of the component comprises Pd with a valence greater or lesser than 2, the required activity of the catalyst of the present invention cannot be achieved.
The valence of the above Pd can be verified by X-ray Photoelectron Spectroscopy (XPS) measurement. XPS is a method for analyzing the state of chemical bond of the atoms present close to the surface of a specimen by irradiating the surface with x-rays and measuring the amount of energy and number of photoelectrons emitted due to the photoelectric effect. Information such as atomic valence can be obtained from the resulting chemical shift. In the analysis of the atomic valence of Pd, Pd3d5/2 peaks with a binding energy of 334-340eV can be employed. Specifically, the above position of the peak for Pd metal is 335.1-335.5 eV, the position of the peak for divalent Pd is 336.3 eV, and the position of the peak for tetravalent Pd is 337.9 eV (xe2x80x9cHand-book of X-ray Photoelectron Spectroscopyxe2x80x9d, Perkin-Elmer Co., (1992)). From these peak positions, it is possible to determine the atomic valence of Pd.
Therefore, the amount for each atomic valence of Pd can be measured by calculating the area of each Pd3d5/2 peak. In the present invention, the percentage of the peak area for divalent Pd in the total sum of the Pd3d5 peak areas calculated in this manner is preferably 80% or more, with 90% or more being particularly preferable.
Although there are no specific limitations to the supported amount of the divalent Pd compound in the catalyst of the present invention, the amount of Pd is preferably 0.01-50 weight %, and even more preferably 0.1-30 weight %, based on the mass of catalyst. If the supported amount is less than 00.1 weight %, activity becomes insufficient. If the supported amount is greater than 50 weight %, the activity per unit mass of Pd easily declines and the use efficiency of the expensive Pd does not increase.
The component (b) of the catalyst of the present invention is at least one element selected from the group consisting of Pt, Ru, Rh, Ir, and Au. There are no specific limitations to the state of these elements; for example metals, oxides, hydroxides, or salts of these elements maybe used. A combination of more than one state may also be used. Among these, oxides and hydroxides are preferable. These elements may be used independently or in combination of two or more as the component (b).
There are no particular limitations to the support amount for the component (b), the mass ratio as a metal in comparison with the component (a) is preferably 0.25 or less. If the mass ratio of the component (b) exceeds 0.25, improved activity cannot be obtained.
As the non-organic porous substance used as the carrier in the catalyst of the present invention, activated carbon, graphite carbon, acetylene black, silica/alumina, titania, zirconia, and the like can be given. Among these, activated carbon, graphite carbon and acetylene black are preferable. These may be used either individually or in combinations of two or more.
The BET specific surface area of the non-organic porous substance is preferably 100 m2/g or more. If the specific surface area is less than 100 m2/g, the dispersion of the components (a) and (b) supported on the non-organic porous substance worsens and the activity tends to decrease.
There are no specific limitations to the preparation method for the catalyst of the present invention. Conventional methods of catalyst preparation such as impregnation, precipitation, and water absorption methods may be used. One example is a simultaneous supporting method by coprecipitation wherein a mixed solution of raw material salts of components (a) and (b) is added to the carrier powder. In another method, first of all, a raw material salt solution of one of the components (a) and (b) is impregnated in the carrier powder and then dried, then the raw material salt solution of the other component is impregnated in the carrier powder and dried. As still another method, a method of mixing a carrier powder that supports the component (a) and a carrier powder that supports the component (b) can be given.
As a starting raw material for the components (a) and (b) used in the preparation of the catalyst of the present invention, chloride, hydrochloride, nitrate, sulfate, organic acid salt, ammine salt, alkaline salt, organic complex, and the like can be given without any specific limitations.
Specifically, as the raw material for the component (a), for example, divalent palladium chloride, sodium chloropalladate, potassium chloropalladate, palladium nitrate, palladium acetate, and the like can be given. Among the raw materials of the component (b), given as the raw materials for Pt are chloroplatinic acid, potassium chloroplatinate, and the like; as the raw materials for Ru, ruthenium chloride, ruthenium nitrate, and the like; as the raw materials for Rh, rhodium chloride, rhodium sulfate, and the like; as the raw material for Ir, iridium sulfate, iridium chloride, and the like; as the raw material for Au, chloroauric acid, sodium gold sulfite, gold acetate, and the like.
The catalyst of the present invention made in the above manner can be used in various types of hydrogenolysis. In particular, hydrogenolysis reaction under low temperature conditions of about room temperature, and debenzylation reaction of the compound in which nitrogen combines with a benzyl group show excellent catalytic effects.